1. Field of the Invention
The present invention relates to a reclosable zipper for use in reclosable plastic bags and packages. More particularly, the present invention relates to a reclosable zipper having a fusible rib layer on each profile.
2. Description of the Prior Art
Reclosable zippers having fusible ribs for sealing the zippers to package material are well known in the reclosable packaging art. Examples of such zippers can be found in U.S. Pat. Nos. 4,673,383, 5,216,787 and 5,242,516.
Fusible ribs offer numerous advantages. For example, as disclosed in U.S. Pat. No. 4,673,383, fusible ribs can minimize the amount of heat and pressure transferred to the body of a zipper and to the package material during sealing of the zipper to the package material, thus minimizing zipper and package distortion. In addition, as disclosed in U.S. Pat. Nos. 5,216,787 and 5,242,516, fusible ribs can be used to bond a zipper to incompatible package material when the fusible ribs are formed of a material which is compatible with the package material and the zipper.
Many prior art zippers which make use of fusible ribs, however, have proven problematic in that it is often difficult to achieve a uniform seal between the zipper and the package material. By way of example, FIG. 1 shows a cross-sectional view of a typical prior art zipper 10 having fusible ribs 24. The zipper includes a male profile 12 interlockable with a female profile 14. The male profile 12 includes a male interlocking member 16 and a flange 18 which extends laterally on either side of the male interlocking member 16 for sealing the male profile 12 to package material (not shown). Likewise, the female profile 14 includes a U-shaped female interlocking member 20 which is interlockable with the male interlocking member 16 and a flange 22 which extends on either side of the female interlocking member 20 for sealing the female profile 14 to the package material.
The male and female flanges 18, 22 each include fusible ribs 24 disposed on flange surfaces 26, 28 directed away from their respective interlocking members 16, 20. The fusible ribs 24 are made of the same material as the rest of the zipper 10. The male and female profiles 12, 14 are sealed to the package material at the fusible ribs 24 via heat and pressure, which heat and pressure causes the fusible ribs 24 to merge into bonding layers between the zipper flanges and the package material, thus sealing the profiles 12, 14 to the package material. Distortion of the zipper and the package material is minimized because the fusible ribs absorb most of the heat and pressure.
However, because of the presence of spaces 30 between the fusible ribs 24, often times the bonding layer which is achieved by the merging of the fusible ribs 24 is not uniform across the widths of the zipper flanges 18, 22. Indeed, there may be portions of the flanges 18, 22 which are not sealed to the package material at all. The result is a relatively weak seal between the profiles 12, 14 and the package material. Additionally, relatively high temperatures are required for sealing, making the zipper unsuitable for high speed reclosable package making applications.
In cases where the zipper is made from a material that is incompatible with the package material, the fusible ribs can be made of a material that is compatible with the package material and zipper, such as a sealant. A typical prior art zipper 32 which employs this type of fusible rib is shown in FIG. 2.
As with the zipper 10 of FIG. 1, the zipper 32 includes a male profile 34 interlockable with a female profile 36. The male profile 34 includes a male interlocking member 38 and a flange 40 which extends laterally on either side of the male interlocking member 38 for sealing the male profile 34 to the package material. Likewise, the female profile 36 includes a U-shaped female interlocking member 42 which is interlockable with the male interlocking member 38 and a flange 44 which extends on either side of the female interlocking member 42 for sealing the female profile 36 to the package material.
The male and female flanges 40, 44 each include fusible ribs 46 disposed on base surfaces 48, 50 directed away from their respective interlocking members 38, 42. The male and female profiles 34, 36 are sealed to the package material at the fusible ribs 46 via heat and pressure. The application of said heat and pressure activates the sealant contained in the fusible ribs 46 and causes the fusible ribs 46 to merge into bonding layers between the zipper flanges and the package material, thus sealing the profiles 34, 36 to the incompatible package material. Once again, the fusible ribs 46 minimize the heat and pressure transferred to the zipper and the package material, thus minimizing zipper and package distortion.
However, as with the zipper 10 of FIG. 1, the presence of sealant-free spaces 52 between the fusible ribs 46 results in non-uniform bonding layers, resulting in a relatively weak seal between the zipper and the package material. And as taught by U.S. Pat. No. 5,216,787, those sealant-free areas are necessary to achieve adequate sealing at a low sealing temperature.
Another technique which is commonly employed to seal reclosable zippers to package material is the use of planar sealant layers, such as disclosed in U.S. Pat. No. 4,835,835. FIG. 3 shows a typical prior art zipper 54 which makes use of such sealant layers 68.
As with the zippers 10, 32 of FIGS. 1 and 2, the zipper 54 includes a male profile 56 interlockable with a female profile 58. The male profile 56 includes a male interlocking member 60 and a flange 62 which extends laterally on either side of the male interlocking member 60 for sealing the male profile 56 to the package material. Likewise, the female profile 58 includes a U-shaped female interlocking member 64 which is interlockable with the male interlocking member 60 and a flange 66 which extends on either side of the female interlocking member 64 for sealing the female profile 58 to package material.
The male and female flanges 62, 66 each include a planar sealant layer 68 disposed on surfaces 70, 72 directed away from their respective interlocking members 60, 64. The male and female profiles 60, 64 are sealed to the package material at the male and female flange surfaces 70, 72 via heat and pressure, which heat and pressure activate the sealant layers 68, thereby sealing the zipper to the package material.
The use of such sealant layers, however, can be problematic in that, as compared to zippers which make use of fusible ribs, larger amounts of heat and pressure applied over a longer period of time are generally needed to fully activate the sealant layers and achieve a uniform seal. This can result in substantial profile and package distortion. Additionally, when sealant layers are used, especially if they are relatively thin, the seal bars tend to cause the sealant to spread unevenly, resulting in uneven and weak seal areas. Further, the longer sealing time makes such zippers unsuitable for high speed applications.
Thus, while the prior art as it relates to fusible ribs and sealant layers is fairly well-developed, it nonetheless remains susceptible to improvement.